Dementia and depression are common problems in geriatric patients and account for many nursing home admissions each year. Mental function loss in the earliest stages of Alzheimer's dementia is often complicated by depression, creating a diagnostic dilemma that hampers treatment and effective coping strategies. Sleep and certain EEG measures are altered in Alzheimer's dementia, perhaps due to degeneration in cholinergic brain pathways. Our initial studies among non-depressed elderly revealed that sleep and EEG variables serve well as markers for early Alzheimer's dementia. This project seeks to confirm and expand these studies, examining these and other potential diagnostic markers in medically healthy communtiy elderly, with and without diagnosable mild Alzheimer's dementia. Sleep and EEG (frequency, power and coherence) measures will be evaluated for two desirable qualities: (1) ability to discriminate mild dementia from non-dementia and (2) ability to discriminate mild dementia from major depression. A major depression subject group will be studied in order to identify and eliminate all measures that are affected in the same way by both depression and dementia. Ability to discriminate mild dementia from non-dementia (or from major depression) will be evaluated using a series of discriminant analyses (DA). Predictor variables emerging in these DAs will be reexamined using previous subject groups in order to replicate results wherever possible. Sensitivity and specificity of the best predictor variables will be calculated. It is possible that useful diagnostic markers for the earliest stages of Alzheimer's dementia may result. A second objective is to further evaluate these predicator variables as correlates of cognitive loss using multiple regression analyses. A series of cognitive tests, covering both dementia and nondementia ranges of cognition will be examined. We hypothesize that primary neuronal degeneration may underlie both cognitive loss and also sleep and EEG changes; this hypothesis would predict that sleep and EEG markers for mild dementia diagnosis will also correlate highly with cognitive loss due to underlying organic changes.